1. Field of the Invention
The present invention relates to a planar plasmon antenna that generates high-intensity near-field light, to a thermally assisted magnetic head and to a hard disk drive.
2. Related Background Art
Thermally assisted magnetic heads for recording magnetic information by applying a magnetic field onto a magnetic recording medium, while heating the latter with near-field light, have attracted attention in recent years. U.S. Pat. No. 7,330,404 discloses such a thermally assisted magnetic head. In the thermally assisted magnetic head, a plasmon antenna comprising a small metal is disposed at a position onto which a laser beam is condensed by a lens. The plasmon antenna generates near-field light upon being irradiated by a laser beam. The longitudinal direction of the plasmon antenna is parallel to the propagation direction of the laser beam. Near-field light of sufficient intensity, however, cannot be obtained with conventional thermally assisted magnetic heads.
“Japanese Journal of Applied Physics Vol. 45, No. 8B, 2006, pp. 6632-6642” discloses a plasmon antenna, comprising a pair of triangular metal films that make up a bow-tie aperture. It is estimated that such a plasmon antenna generates near-field light of relatively high intensity. Two or more near-field light peaks are observed in plasmon antennas with such a geometry. The above prior art document describes the feature to the effect that a single triangular metal film can be used as the plasmon antenna, although in that case peak intensity is expected to be not high, unlike in the case of two triangular metal films.